Helicopter blade mandrel

ABSTRACT

Methods and apparatus are provided for making a rotor blade spar from composite material wherein a multi-component mandrel is used to form the composite spar. The mandrel is made using a number of components, which are assembled to provide a structure that is sufficiently strong to maintain the spar shape during pre-cure lay up, compaction and curing of the composite material. The multiple components used to form the mandrel can be separated from each other and easily removed from the spar either before or after curing of the composite material. The mandrel components can then be re-assembled and re-used to form additional composite spars.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to helicopter rotor blades thatare made from composite materials. More particularly, the presentinvention is directed to the processes and apparatus that are used inthe manufacture of such composite rotor blades.

2. Description of Related Art

Rotor blades are a critical component of every helicopter. The rotorblades are subjected to a complex set of rather extreme aerodynamicforces that vary continually during flight. The rotor blades function asrotating airfoils or wings that are shaped to provide the aerodynamiclift required for a given aircraft. Rotor blades typically include aspar that extends from the root of the rotor blade to its tip. The sparis a major structural element of the rotor blade that provides the bladewith the structural strength needed to carry high operational loads.

The typical rotor blade spar is a long tubular structure around whichthe rest of the blade is formed. The spar tube has an ellipticalcross-section that is formed to provide a forward or leading edge andrearward or trailing edge. In order to provide optimum aerodynamicperformance, many spar tubes include a slight twist about thelongitudinal axis. Typical twists in the spar provide rotations of theelliptical cross-section of up to 10 degrees and more as one moves fromthe root of the rotor blade to its tip. In addition, the ellipticalshape of the spar cross-section may be varied from the spar root to thespar tip to meet a variety of aerodynamic and structural loadingparameters.

High strength materials, such as titanium and aluminum alloys, havetypically been used to make rotor blades. These high strength metalmaterials are particularly well suited for forming the rotor blade spar.Titanium has been routinely formed into the relatively long, tubularspar structure and machined or otherwise fabricated to provide a complexvariety of twists and varying cross-sectional shapes.

Composite materials have also been used to form rotor blade spars. Thecombination of light weight and structural strength have made compositesa popular choice for making not only the rotor blade spar, but theentire rotor blade. Exemplary composite rotor blades and the processesfor making them are described in U.S. Pat. Nos. 4,892,462; 5,346,367;5,755,558; and 5,939,007.

The typical composite spar is fabricated by applying the uncuredcomposite material to the surface of a long cylindrical mold or mandrelthat is shaped to provide the interior surface of the spar tube. Afterthe composite material is applied to the mold or mandrel, it iscompacted and cured at an elevated temperature to provide the final sparstructure. A problem associated with making composite spars revolvesaround what to do with the mold or mandrel once the spar has beenformed. The length of the mold and the variations in ellipticalcross-section of the spar, as well as any twist in the spar, make itvery difficult to remove the mold or mandrel after the spar has cured.

One approach to solving the mold/mandrel removal problem has been tomake a mold out of a material that is strong enough to maintain itsshape during pre-cure fabrication of the composite spar, but whichdisintegrates or otherwise shrinks during the cure cycle so that it canbe removed from the spar cavity or simply left in place. For example, avariety of foams have been used alone or in combination with anunderlying hard mandrel structure to provide a suitable spar mold. Thefoam melts or otherwise shrinks to a fraction of its initial size duringcuring at elevated temperatures. The resulting shrunken mold issufficiently small so that it can be removed from the spar cavity orleft in place.

Although foam molds have been used successfully in fabricating compositespars for rotor blades, it is many times difficult to find a foam orother material that has the needed structural strength to maintaincritical spar dimensions during formation of the spar, while at the sametime being able to deteriorate relatively rapidly during cure. Inaddition, the mold can only be used once, which adds considerably to thecost of spar fabrication.

SUMMARY OF THE INVENTION

In accordance with the present invention, methods and apparatus areprovided for making a rotor blade spar from composite material wherein amulti-component mandrel is used to form the composite spar. The mandrelis made using a number of components, which are assembled to provide astructure that is sufficiently strong to maintain the spar shape duringpre-cure lay up, compaction and curing of the composite material. Themultiple components used to form the mandrel can be separated from eachother and easily removed from the spar either before or after curing ofthe composite material. The mandrel components can then be re-assembledand re-used to form additional composite spars.

As a feature of the present invention, a multi-component mandrel isprovided for use in molding a helicopter blade wherein the rotor bladeincludes a spar that extends parallel to the longitudinal axis of therotor blade. The spar that is being formed includes interior surfacesthat form a spar cavity that also extends longitudinally from the rootof the blade to the tip. The spar interior surfaces include a leadingedge surface that is composed of an upper leading edge portion and alower leading edge portion. The spar interior surfaces further include atrailing edge surface that is composed of an upper trailing edge portionand a lower trailing edge portion. The spar interior surfaces alsoinclude an upper surface that extends between the leading edge upperportion and the trailing edge upper portion, as well as a lower surfacethat extends between the leading edge lower portion and the trailingedge lower portion.

The mandrel is made up of a forward component that includes an exteriorsurface that is shaped to provide the leading edge surface of the sparinterior surface. The forward component includes an upper rear edge thathas an outer surface, which is shaped to provide the upper leading edgeportion of the spar interior surfaces. The forward component alsoincludes a lower rear edge that is shaped to provide the lower leadingedge portion of the spar interior surfaces. The mandrel also includes arearward component that is shaped to provide the trailing edge surfaceof the spar interior surfaces. The rearward component includes an upperforward edge that is shaped to provide the upper trailing edge portionof the spar interior surfaces. The rearward component also includes alower forward edge that is shaped to provide the lower trailing edgeportion or the spar interior surfaces.

The forward and rearward components of the mandrel are connectedtogether by an upper component and a lower component. The uppercomponent is shaped to provide the upper surface of said spar interiorsurfaces. The upper component includes a forward edge that is connectedto the upper rear edge of the forward component and a rearward edge thatis connected to the upper forward edge of the rearward component. Thelower component is shaped to provide the lower surface of said sparinterior surfaces. The lower component includes a forward edge that isconnected to the lower rear edge of the forward component and a rearwardedge that is connected to the lower forward edge of said rearwardcomponent.

The final component of the mandrel is a support structure that islocated between the upper component and the lower component. The supportstructure provides reinforcement for the upper and lower components andalso holds them in place against the forward and rearward components. Asa feature of the present invention, the support structure is collapsiblewhen a tensioning force is applied to the support structure along thelongitudinal axis of said rotor blade. The collapsing of the supportstructure allows it to be removed from the spar cavity. Once the supportstructure is removed, the upper and lower components of the mandrel canbe disconnected from the forward and rearward components. The componentscan then be removed individually from the spar cavity.

The present invention also covers methods for making the multi-componentmandrel as well as the methods for molding composite rotor blade sparsusing the multi-component mandrel and the resulting rotor blade spar.The multi-component mandrel of the present invention provides a numberof advantages over existing methods for making composite rotor blades.These advantages include the ability to withstand the forces applied tothe mandrel during fabrication of the composite blade in order to avoidany undesirable variations in blade shape. In addition, the mandrel canbe used to form complex spar shapes including spars with varying degreesof twist and changes in elliptical cross-sectional geometry. A furtheradvantage is that the mandrel can be re-assembled and used repeatedly.

The above described and many other features and attendant advantages ofthe present invention will become better understood by reference to thefollowing detailed description when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of an exemplary compositehelicopter rotor blade that includes a spar that can be made using themulti-component mandrel in accordance with the present invention.

FIG. 2 is a perspective view of a preferred exemplary multi-componentmandrel in accordance with the present invention.

FIG. 3 is a sectional of view of a portion of FIG. 2 taken in the 3-3plane

FIG. 4 is the same view as FIG. 3 except that the composite materialspar is shown in place on the exterior surface of the mandrel.

FIG. 5 is a cross-sectional view of the mandrel depicting how thecomponents are separated for removal from the spar after compactionand/or curing of the composite spar.

DETAILED DESCRIPTION OF THE INVENTION

A preferred exemplary multi-component mandrel in accordance with thepresent invention for use in molding a helicopter rotor blade fromcomposite material is shown generally at 10 in FIG. 2. An exemplaryhelicopter rotor blade that can be molded utilizing the mandrel 10 isshown in a simplified form in FIG. 1 at 12. The rotor blade 12 includesa spar 14 that extends parallel to the longitudinal axis 16 of the rotorblade 12. The spar 14 typically extends from the root of the rotor blade(not shown) to the tip 18. The spar 14 is a tubular structure that hasan elliptically shaped cross-section as shown in FIG. 1. The spar 14includes a number of interior surfaces that are formed by the mandrel10. These interior spar surfaces define the spar cavity 20.

Referring to FIG. 1, the spar interior surfaces are composed of aleading edge surface 22, trailing edge surface 24, an upper surface 26and a lower surface 28. The leading edge surface 22 includes an upperleading edge portion 30 and a lower leading edge portion 32. Thetrailing edge surface 24 includes an upper trailing edge portion 34 andlower trailing edge portion 36. The upper surface 26 extends between theupper leading edge portion 30 and the upper trailing edge portion 34.The lower surface 28 extends between the lower leading edge portion 32and the lower trailing edge portion 36.

Referring to FIG. 2, the mandrel 10 includes a forward component 38 thathas an exterior surface, which is shaped to provide the spar interiorleading edge surface 22. The mandrel forward component 38 includes anupper rear edge 40 that has an exterior surface, which is shaped toprovide the upper leading edge portion 30 of the spar. The mandrelforward component 38 also includes a lower rear edge 42 that has anexterior surface, which is shaped to provide the lower leading edgeportion 32 of the spar.

The mandrel 10 also includes a rearward component 44 that has anexterior surface, which is shaped to provide the spar interior trailingedge 24. The mandrel rearward component 44 includes an upper forwardedge 46 that has an exterior surface, which is shaped to provide theupper trailing edge portion 34. The mandrel rearward component 44 alsoincludes a lower forward edge 48 that has an exterior surface, which isshaped to provide the lower trailing edge portion 36.

The mandrel 10 further includes an upper component 50 that has anexterior surface, which is shaped to provide the spar upper interiorsurface 26. The upper component 50 includes a forward edge 52 that isconnected to the upper rear edge 40 of the forward component 38. Theupper component 50 also includes a rearward edge 54 that is connected tothe upper forward edge 46 of the rearward component 44. The mandrel 10also includes a lower component 56 that has an exterior surface, whichis shaped to provide the spar lower interior surface 28. The lowercomponent 56 includes a forward edge 58 that is connected to the lowerrear edge 42 of the forward component 38. The lower component 56 alsoincludes a rearward edge 60 that is connected to the lower forward edge48 of the rearward component 44.

The final component of mandrel 10 is a collapsible support structure,which is shown in FIG. 2 as corrugated support strips 62 and 64. Thecorrugated support strips 62 and 64 extend longitudinally within themandrel 10 (i.e. parallel to the longitudinal axis 16 of the spar). Thecorrugated support strips 62 and 64 are located within the mandrelcavity so as to provide an outward bias against the upper component 50and lower component 56 and to provide support for these two componentsalong their entire lengths. As can be seen from FIG. 2, the forward andrearward edges 52 and 54 of the upper component 50 are shaped so thatthey overlap on the inside of the upper rear edge 40 of the forwardcomponent 38 and upper forward edge 46 of the rearward component 44,respectively. This overlapping arrangement provides for a secure, butreleasable, connection between the upper component 50 and the forwardand rearward components 38 and 44. Likewise, the forward and rearwardedges 58 and 60 of the lower component 56 are shaped so that theyoverlap on the inside of the lower rear edge 42 of the forward component38 and lower forward edge 48 of the rearward component 44, respectively.This overlapping arrangement also provides for a secure, but releasable,connection between the lower component 56 and the forward and rearwardcomponents 38 and 44.

The outward bias provided by the corrugated strips 62 and 64 against theupper and lower mandrel components 50 and 56 provides compressionconnections along the four locations where the mandrel componentsoverlap as described above. These compression connections keep themandrel in the form of a single relatively strong structure duringfabrication of the composite spar. Upon removal of the corrugatedsupport strips 62 and 64, the upper and lower components 50 and 56 maybe move toward each other and disconnected from the forward and rearwardcomponents 38 and 44.

The collapsible support structure must be sufficiently strong to preventthe upper and lower components from collapsing together during lay up,compaction and curing of the composite spar. At the same time, thesupport structure must be able to collapse laterally when a tensioningforce is applied to it along the longitudinal axis of the rotor blade.The term “collapsible” is used herein to mean that the structure must,as a minimum, be able to collapse a sufficient amount to reduce thefriction between the support structure and the upper/lower components,so that the support structure may be pulled longitudinally from the rootend of the spar cavity. In other words, the support structure must beable to collapse enough, when pulled from one end, to unlock the supportstructure from its friction fit against the upper and lower components.

Corrugated strips, as shown in FIG. 2 are the preferred collapsiblesupport structure. However, other types of materials may be usedprovided that they meet the above criteria with respect to lateralshrinkage when a longitudinal tensioning force is applied. It should benoted that two corrugated strips 62 and 64 are shown in FIG. 2 as beingpreferred. However, a single corrugated strip may be used, especially insituations where the geometry of the spar cavity is not complex.Alternatively, more than two strips may be used, if desired.

The corrugated strips may be made from any material that provides thedesired combination of strength and flexibility. It is preferred thatthe corrugated strips be sufficiently resilient that they are notdeformed when they are collapsed and removed from the mandrel cavity byapplication of longitudinal tension. This allows the strips to used morethan once as the collapsible support structure. A wide variety of metalsare available that have the necessary strength and flexibility tofunction as a support structure. However, it is preferred that thecorrugated strips be made from composite material. Composite materialsprovide the strength necessary to keep the upper and lower componentsfrom collapsing during application of external pressure during thecompaction and curing processes. In addition, corrugated strips madefrom composite materials have sufficient flexibility and resiliency tocollapse the desired amount when longitudinal tension is applied andthen spring back to their original shape.

FIG. 3 is a sectional view that shows a portion of the corrugated strip64 in place between the upper and lower components 50 and 56 of themandrel 10. The corrugated strip 64 has ridges 66 which extendsubstantially perpendicular to the longitudinal axis 16 of the spar 14.Spacers 68 may be placed between the ridges 66 of the corrugated stripand the upper and lower components 50 and 56 to facilitate removal ofthe corrugated strip 64 from the mandrel. Use of spacers 68 to enhancerelease of the ridges 66 from the upper and lower components 50 and 56is preferred, but not required. The spacers 68 may be used on all orsome of the ridges 66. The spacers 68 may be in the form of singleelongated strips or they may be in the form of multiple washers that arespaced along the ridges. The spacers 68 made from fiber reinforcedpolyamide or phenolic are preferred. However, the spacers can be madefrom a variety of materials provided that the surface tension issufficiently low so that the washers are released from the mandrelsurfaces when the corrugated strip is removed. Materials, such aspolytetrafluorethylene and other non-sticking substances, may be used,but are not particularly preferred because they can be difficult to keepin place on the ridges of the corrugated strips during mandrel assembly.

The washers are preferably kept in place on the ridges using a smallamount of glue or other binder material that is sufficient to hold thewasher in place during mandrel fabrication, but which allows the washersto be released from the ridges when the mandrel is removed from the sparcavity. In addition, it is preferred that the ridges be machinedslightly in order to form platforms for seating the washer. The degreeof machining depends upon the size of the washer and the thickness ofthe corrugated support material. The washers are typically on the orderof a few thousandths of an inch thick to a few tenths of an inch thickor even thicker depending upon the particular mandrel dimensions and thedegree to which the corrugated ridges are machined to accept the washer.

As shown in FIG. 3, it is preferred that the spacers 68 are located ononly one side of the corrugated strip. The spacers 68 are shown locatedon the top ridges in FIG. 3 for demonstrative purposes only. The spacers68 could alternatively be located on the bottom ridges. During assemblyof the mandrel, it is preferred that the corrugated strip 64 betemporarily attached to the lower component 56 using removablefasteners. The removable fasteners, such as clecos, are used to connectthe lower ridges of the corrugated strip to the lower component. Thewashers 68 are placed on the upper ridges of the corrugated strip 68 andthen the upper component 50 is put in place. In order to hold theassembly of components together, it is preferred to wrap the completedassembly, as shown in FIG. 3, in shrink-wrap or other suitable tape.

FIG. 4 shows a partial cross-sectional view of the mandrel 10 locatedwithin the composite spar 14 just after compaction and/or curing of thecomposite material. Arrow 70 depicts the application of a tensioningforce (i.e. pull) along the longitudinal axis of the rotor blade. Arrows72 depict the collapsing of the corrugated strip 64 that results fromthe longitudinal pull on the strip. As is apparent, the ridges 66 onlyneed to collapse in the direction of arrows 72 a sufficient amount torelease washers 68, so that the strip 64 may be pulled longitudinallyfrom the mandrel. This allows for the corrugated strip 64 to be deformedthe minimum amount so that it can be reused a number of times. In somesituations, especially with very complex spar geometries, it may benecessary to apply sufficient tension 70 in order to substantiallycollapse the corrugated strip in order to be able to remove it from themandrel.

FIG. 5 is a simplified side cross-sectional view that shows the mandrel10 in place after the corrugated supports strips 62 and 64 have beenremoved. The upper and lower components 50 and 56 are moved inwardtowards each other, as represented by arrows 74, so that they can beremoved from the spar cavity 20. The forward and rearward components 38and 44 are also moved inward towards each other, as represented byarrows 76, so that they also can be removed from the spar cavity 20.

The mandrel 10 may be removed from the spar cavity 20, as describedabove, either after compaction of the uncured spar composite materialaround the mandrel or after the compacted composite spar has been cured.It is preferred to remove the mandrel prior to curing in order tomaximize the number of times it can be re-used. The mandrel should beable to withstand the pressures that are present during normalprocedures for molding helicopter rotor blade spars. Typically, themandrel should be able to withstand external pressures on the order of10 to 15 inches of Hg and higher. The mandrel should also be able towithstand the temperatures at which the composite materials used to makethe spar are cured. Typically, such composites are cured at temperaturesin the range of 120° C. to 200° C. and even higher.

The materials that are used to make the four external components of themandrel 10 may also be any of the metals typically used for makingmandrels for molding composite materials. However, as was the case withthe corrugated support strips, composite materials are a preferredmaterial for making the external mandrel components that actually comein contact with the spar during rotor blade fabrication. The externalsurfaces of the mandrel or the shrink-wrap (if used) may be coated witha suitable release agent, if desired.

The composite materials that may be used to make the mandrel componentsinclude those containing glass or carbon fibers. The fibers may be inthe form of woven fabric, unidirectional fibers or randomly orientedfibers. Any of the various thermosetting resins that are suitable foruse in relatively high temperature molding operations may be used as thematrix material. Exemplary resins include epoxies, phenolics,bismaleimides and polyester. A preferred material is an isotropiccomposite material that is composed of randomly oriented chips ofunidirectional fibers in an epoxy matrix. This type of mandrel materialis available from Hexcel Corporation (Dublin, Calif.) under thetradename HexMC®. An alternate preferred material for use in making themandrel components is carbon fabric/epoxy prepreg, such as HEXCEL 8552,which is also available from Hexcel Corporation (Dublin, Calif.). Bothof these materials are supplied as uncured prepregs, which can be formedinto the desired mandrel component and cured according to conventionalmethods for fabricating and curing epoxy-based composite structures.

As an example, the mandrel of the present invention may be used to moldthe spar of a helicopter rotor blade where the spar is on the order of20 to 25 feet long or even longer for large helicopters. The distancebetween the leading edge and trailing edge of the spar at the blade rootranges from a few inches to two feet or more. This distance tapers downto a few inches to a foot or more at the blade tip. The thickness of thespar at the blade root ranges from an inch to a foot or more and tapersdown to less than an inch or up to a few inches at the blade tip. Thespar has a twist on the order 10 degrees about its longitudinal axisfrom the root of the spar to its tip. The various external components ofthe mandrel (forward component, rearward component, upper component andlower component) are made to match the internal shape of the spar. Theyare fabricated as four individual components that are each 20 to 25 feetlong. Each component is made from a sufficient number of plies of Hexcel8552 carbon/epoxy prepreg or HexMC® to make components that are from0.01 inch thick to 0.5 inch thick or more depending upon the size of themandrel. The components are cured according to conventional curingprocedures.

For the exemplary mandrel described herein, two corrugated supportstrips are used that are both 20 to 25 feet long to match the length ofthe other mandrel components. The corrugated support strips are sized sothat the lateral distances between the ridges match the thickness of themandrel as it varies from root to tip and from leading edge to trailingedge. The two corrugated support strips are positioned inside themandrel cavity so that they apply the proper outward bias force againstthe upper and lower components over the entire length of the mandrel.The longitudinal distance between the individual upper ridges on thecorrugated strip should be sufficeint to provide the needed support forthe upper and lower components. The longitudinal distance between thelower ridges on the corrugated strip should be about the same as thedistance between the upper ridges. The longitudinal distances betweenthe ridges may vary form the root to the tip. For example, it may bedesirable to make the ridges closer together nearer the root of themandrel in order to provide added support where the spar cavity has thelargest cross-sectional area.

The corrugated strips are also made from HEXCEL 8552 carbon/epoxyprepreg or HexMC®, which are also formed into the required corrugatedshape and compacted and cured according to conventional curingprocedures. The resulting corrugated strips should be sufficiently thickto provide support for the upper and lower components during compactionand curing, if desired. The composite corrugated strips should be madefrom a sufficient number of prepreg plies to provide corrugated stripsthat are strong enough to withstand the pressures to which the sparcomposite material and underlying mandrel are subjected to duringstandard compaction procedures and curing.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the present invention.Accordingly, the present invention is not limited by the above-describedembodiments, but is only limited by the following claims.

1. A mandrel for use in molding a helicopter rotor blade wherein saidrotor blade includes a spar that extends parallel to the longitudinalaxis of said rotor blade, said longitudinal axis extending from the rootof said rotor blade to the tip of said rotor blade, said spar havinginterior surfaces that defines a spar cavity that also extendslongitudinally from the root of said rotor blade to the tip of saidrotor blade, said spar interior surfaces including a leading edgesurface that comprises an upper leading edge portion and a lower leadingedge portion, a trailing edge surface that comprises an upper trailingedge portion and a lower trailing edge portion, an upper surface thatextends between said leading edge upper portion and said trailing edgeupper portion and a lower surface that extends between said leading edgelower portion and said trailing edge lower portion, said mandrelcomprising: a forward component that comprises an exterior surface thatis shaped to provide said leading edge surface of said spar interiorsurfaces, said forward component comprising an upper rear edgecomprising an outer surface that is shaped to provide said upper leadingedge portion and a lower rear edge that is shaped to provide said lowerleading edge portion; a rearward component that is shaped to providesaid trailing edge surface of said spar interior surfaces, said rearwardcomponent comprising an upper forward edge that is shaped to providesaid upper trailing edge portion and a lower forward edge that is shapedto provide said lower trailing edge portion; an upper component that isshaped to provide said upper surface of said spar interior surfaces,said upper component comprising a forward edge that is connected to saidupper rear edge of said forward component and a rearward edge that isconnected to said upper forward edge of said rearward component; a lowercomponent that is shaped to provide said lower surface of said sparinterior surfaces, said lower component comprising a forward edge thatis connected to said lower rear edge of said forward component and arearward edge that is connected to said lower forward edge of saidrearward component; and a collapsible support structure located betweensaid upper component and said lower component, said support structurebeing collapsible when a tensioning force is applied to said supportstructure along the longitudinal axis of said rotor blade, saidcollapsible support structure comprising a corrugated material thatcomprises ridges which extend substantially perpendicular to saidlongitudinal axis wherein said ridges are friction fit against the upperand lower components.
 2. A mandrel for use in molding a helicopter rotorblade according to claim 1 wherein said collapsible support structurecomprises a forward piece of corrugated material and a rearward piece ofcorrugated material.
 3. A mandrel for use in molding a helicopter rotorblade according to claim 1 wherein said corrugated material comprises acomposite material.
 4. A mandrel for use in molding a helicopter rotorblade according to claim 1 wherein said corrugated material comprises aforward edge and a rearward edge and wherein the lateral distancebetween the ridges of said corrugated material decreases from theforward edge of said corrugated material to the rearward edge of saidcorrugated material.
 5. A mandrel for use in molding a helicopter rotorblade according to claim 1 wherein the connections between said forwardcomponent and said upper and/or lower components are releasableconnections.
 6. A mandrel for use in molding a helicopter rotor bladeaccording to claim 1 wherein the connections between said rearwardcomponent and said upper and/or lower components are releasableconnections.
 7. A mandrel for use in molding a helicopter rotor bladeaccording to claim 1 wherein the forward edge of said upper componentoverlaps the upper rearward edge of said forward component on the insidethereof and wherein the forward edge of said lower component overlapsthe lower rearward edge of said forward component on the inside thereof.8. A mandrel for use in molding a helicopter rotor blade according toclaim 1 wherein the rearward edge of said upper component overlaps theupper forward edge of said rearward component on the inside thereof andwherein the rearward edge of said lower component overlaps the lowerforward edge of said rearward component on the inside thereof.